Thermometer

ABSTRACT

A carbon atmosphere thermometer  10   a  has: a thermocouple having thermocouple wires  16, 18,  a thermocouple temperature measuring junction  14,  and an insulating tube  12;  a first protection tube  20  surrounding the thermocouple, while at least partially spaced apart from the thermocouple wires  16, 18  and others of the thermocouple; and a second protection tube  22  surrounding the first protection tube  20,  while at least partially spaced apart from the first protection tube  20.  For this reason, it becomes feasible to protect the thermocouple from the external environment, while preventing the thermocouple from reacting with the first protection tube  20.  Furthermore, it becomes feasible to protect the thermocouple and the first protection tube  20  from the external environment, while preventing the first protection tube  20  from reacting with the second protection tube  22.

TECHNICAL FIELD

The present invention relates to a thermometer and, particularly, to athermometer having a thermocouple and protection tubes.

BACKGROUND ART

In transportation-related sections and aerospace fields, activedevelopment of carbon-based materials has been conducted in recentyears, for the purposes of energy saving based on weight reduction andCO₂ emission control. Furthermore, SiC, which is a compound of carbonand silicon, is also acknowledged as an engineering ceramic and powersemiconductor with very high characteristics and is already developed toa practical level. The advantages of the carbon-based materials includelight weight, high strength, high specific strength, good heatconductivity, and, high heat resistance because of the high meltingpoint of carbon itself.

Such materials are generally manufactured in a high temperature rangeover 1800° C. On this occasion, stable manufacture at high yieldsbecomes possible with execution of temperature control duringmanufacture and thus it is an urgent necessity to develop a temperaturemeasuring method in the high temperature range. A conventionaltemperature measuring method is a method using a radiation thermometer.However, temperature measurement is impossible in situations where anobstacle lies between the radiation thermometer and a temperaturemeasurement target. In addition, it has other problem that temperaturemeasurement accuracy considerably worsens in situations where infraredrays radiated from the temperature measurement target are absorbed bygas or the like.

As a solution to the foregoing problems of the radiation thermometer,there is a method making use of a thermometer using a thermocouple.Temperature measurement by the thermocouple is a method of combiningwires of dissimilar materials to measure a thermoelectromotive forcegenerated by a temperature difference in a circuit. In the temperaturemeasurement by the thermocouple, the thermocouple can be installed inthe vicinity of the temperature measurement target because thethermocouple consists of the wires, and thus it can measure temperatureswith accuracy.

A tungsten-rhenium (WRe) thermocouple is known as a thermocouple forhigh-temperature measurement and can measure ultra-high temperaturesaround 3000° C. in vacuum, reductive, and inert atmospheres. Aniridium-iridium rhodium (Ir-IrRh) thermocouple can measure temperaturesup to around 2200° C. even in an oxidative atmosphere if the measurementis performed in short time, as well as in the vacuum, reductive, andinert atmospheres. However, under circumstances where the thermocoupleis exposed to a carbon-existing atmosphere at high temperatures or undercircumstances where the thermocouple touches carbon at hightemperatures, the wires of the thermocouple react with carbon to changethe thermoelectromotive force and, for this reason, it is difficult touse the thermocouple without protection for the wires.

It is thus common practice to provide a protection tube surrounding thethermocouple, to protect the thermocouple. For example, Patent Document1 discloses the protection tube surrounding the thermocouple, which isthe protection tube having a double-layered structure wherein portionsconstituting an inner peripheral wall and an outer peripheral wall ofthe protection tube have different compositions. In the protection tubeof Patent Document 1, the inner peripheral wall of the protection tubeis comprised of a material such as silicon nitride (Si₃N₄) withexcellent heat resistance and high thermal conductivity. The outerperipheral wall of the protection tube is comprised of a ceramicmaterial such as mixture of magnesia (MgO) particles and carbon (C)particles poorly reactive with temperature measurement objects. Theinner peripheral wall and outer peripheral wall of the protection tubeare comprised of respective sintered bodies, which are obtained by suchintegral firing as to adhere the inside sintered body and the outsidesintered body to each other.

PRIOR ART DOCUMENTS Patent Document

Patent Document 1: Japanese Unexamined Patent Publication No. 2000-55740

SUMMARY OF INVENTION Problems to be Resolved by the Invention

In the case of the protection tube of the multilayer structure asdisclosed in Patent Document 1, however, reaction occurs between thematerial of the outer peripheral wall and the material of the innerperipheral wall, particularly, in the high temperature range, and it isthus difficult to protect the wires of the thermocouple over a longperiod of time.

The present invention has been accomplished in view of the above problemand it is an object of the present invention to provide a thermometercapable of protecting the thermocouple from the external environment,while preventing the layers of the protection tube from reacting witheach other.

Means of Solving the Problems

One embodiment of the present invention is a thermometer comprising: athermocouple having a pair of wires, a temperature measuring junctionbetween the wires, and an insulator covering the wires; a firstprotection tube surrounding the wires, the temperature measuringjunction, and the insulator of the thermocouple, while at leastpartially spaced apart from the wires, the temperature measuringjunction, and the insulator of the thermocouple; and a second protectiontube surrounding the first protection tube, while at least partiallyspaced apart from the first protection tube.

In this configuration, the thermometer comprises: the thermocouplehaving the pair of wires, the temperature measuring junction between thewires, and the insulator covering the wires; the first protection tubesurrounding the wires, the temperature measuring junction, and theinsulator of the thermocouple, while at least partially spaced apartfrom the wires, the temperature measuring junction, and the insulator ofthe thermocouple; and the second protection tube surrounding the firstprotection tube, while at least partially spaced apart from the firstprotection tube. The first protection tube surrounds the wires, thetemperature measuring junction, and the insulator of the thermocouple,while at least partially spaced apart from the wires, the temperaturemeasuring junction, and the insulator of the thermocouple. For thisreason, while preventing the thermocouple from reacting with the firstprotection tube, the thermocouple can be protected from the externalenvironment. Furthermore, the second protection tube surrounds the firstprotection tube, while at least partially spaced apart from the firstprotection tube. For this reason, while preventing the first protectiontube from reacting with the second protection tube, the thermocouple andthe first protection tube can be protected from the externalenvironment.

In this case, at least either of an interior of the first protectiontube or a space between the first protection tube and the secondprotection tube may be filled with an inert gas.

In this configuration, at least either of the interior of the firstprotection tube or the space between the first protection tube and thesecond protection tube is filled with the inert gas. For example, whenthe interior of the first protection tube is filled with the inert gas,an interior of an insulating tube as the insulator covering the wires,i.e., an atmosphere around the wires is also the inert gas. Even in acase where a hollow member with an open or closed end face is disposedaround the temperature measuring junction, the atmosphere around thetemperature measuring junction and the wires is the inert gas. For thisreason, it is feasible to effectively prevent reaction between thethermocouple and the first protection tube or reaction between the firstprotection tube and the second protection tube.

Furthermore, the thermometer may further comprise third protection tubelocated outside the first protection tube and inside the secondprotection tube and surrounding the first protection tube, while atleast partially spaced apart from the first protection tube and thesecond protection tube.

In this configuration, the thermometer further comprises the thirdprotection tube located outside the first protection tube and inside thesecond protection tube and surrounding the first protection tube, whileat least partially spaced apart from the first protection tube and thesecond protection tube. For this reason, it is feasible to effectivelyprevent the first protection tube from reacting with the secondprotection tube, while preventing the first protection tube and thesecond protection tube from reacting with the third protection tube.

In this case, at least any one of an interior of the first protectiontube, a space between the first protection tube and the third protectiontube, and a space between the second protection tube and the thirdprotection tube may be filled with an inert gas.

In this configuration, at least any one of the interior of the firstprotection tube, the space between the first protection tube and thethird protection tube, and the space between the second protection tubeand the third protection tube is filled with the inert gas. As describedabove, for example, when the interior of the first protection tube isfilled with the inert gas, the interior of the insulating tube as theinsulator covering the wires, i.e., the atmosphere around the wires isalso the inert gas. Even in the case where a hollow member with an openor closed end face is disposed around the temperature measuringjunction, the atmosphere around the temperature measuring junction andthe wires is the inert gas For this reason, it is feasible toeffectively prevent reaction between the thermocouple and the firstprotection tube, reaction between the first protection tube and thethird protection tube, and reaction between the second protection tubeand the third protection tube.

In the thermometer comprising the first protection tube and the secondprotection tube, the first protection tube may contain any one of Mo, W,Ta, and Ir and the second protection tube may contain any one ofgraphite, C/C composite, glassy carbon, SIC, and BN.

In this configuration, since the first protection tube contains any oneof Mo, W, Ta, and Ir having low reactivity with the thermocouple and thesecond protection tube, the lifetime of the thermocouple can be improvedwhile the thermocouple is certainly protected from the externalenvironment. Since the second protection tube contains any one ofgraphite, C/C composite, glassy carbon, SiC, and BN having lowreactivity with carbon in an atmosphere and the first protection tube,the thermocouple and the first protection tube can be certainlyprotected from the external environment.

In the thermometer comprising the first protection tube and the secondprotection tube, the first protection tube may contain any one of Mo, W,Ta, and Ir and the second protection tube may contain any one ofgraphite, C/C composite, glassy carbon, SiC, BN, Al₂O₃, vitreous carbon,pyrolytic carbon-coated graphite, vitreous carbon-coated graphite, andPBN (pyrolytic boron nitride).

In this configuration, since the first protection tube contains any oneof Mo, W, Ta, and Ir having low reactivity with the thermocouple and thesecond protection tube, the lifetime of the thermocouple can be improvedwhile the thermocouple is certainly protected from the externalenvironment. Since the second protection tube contains any one of theforegoing graphite, C/C composite, glassy carbon, SiC, and BN, or,contains any one of Al₂O₃, vitreous carbon, pyrolytic carbon-coatedgraphite, vitreous carbon-coated graphite, and PBN having the sameeffect as the foregoing materials, the thermocouple and the firstprotection tube can be certainly protected from the externalenvironment.

In the thermometer comprising the first protection tube, the secondprotection tube, and the third protection tube, the first protectiontube may contain any one of Mo, W, Ta, and Ir, the second protectiontube may contain any one of graphite, C/C composite, glassy carbon, SiC,and BN, and the third protection tube may contain any one of Mo, W, Ta,Nb, and Ir.

In this configuration, since the first protection tube contains any oneof Mo, W, Ta, and Ir having low reactivity with the thermocouple and thethird protection tube, the lifetime of the thermocouple can be improved.Since the second protection tube contains any one of graphite, C/Ccomposite, glassy carbon, SiC, and BN having low reactivity with carbonin an atmosphere and the third protection tube, the thermocouple, thefirst protection tube, and the third protection tube can be certainlyprotected from the external environment. Furthermore, since the thirdprotection tube contains any one of Mo, W, Ta, Nb, and Ir having lowreactivity with the first protection tube and the second protectiontube, the thermocouple and the first protection tube can be certainlyprotected from the external environment.

In the thermometer comprising the first protection tube, the secondprotection tube, and the third protection tube, the first protectiontube may contain any one of Mo, W, Ta, and Ir, the second protectiontube may contain any one of graphite, C/C composite, glassy carbon, SiC,BN, Al₂O₃, vitreous carbon, pyrolytic carbon-coated graphite, vitreouscarbon-coated graphite, and PBN, and the third protection tube maycontain any one of Mo, W, Ta, Nb, Ir, graphite, C/C composite, SiC,glassy carbon, vitreous carbon, pyrolytic carbon-coated graphite,vitreous carbon-coated graphite, BN, and PBN.

In this configuration, since the first protection tube contains any oneof Mo, W, Ta, and Ir having low reactivity with the thermocouple and thethird protection tube, the lifetime of the thermocouple can be improved.Since the second protection tube contains any one of the foregoinggraphite, C/C composite, glassy carbon, SiC, and BN, or, contains anyone of Al₂O₃, vitreous carbon, pyrolytic carbon-coated graphite,vitreous carbon-coated graphite, and PBN having the same effect as theforegoing materials, the thermocouple, the first protection tube, andthe third protection tube can be certainly protected from the externalenvironment. Furthermore, since the third protection tube contains anyone of Mo, W, Ta, Nb, and Ir, or, contains any one of graphite, C/Ccomposite, SiC, glassy carbon, vitreous carbon, pyrolytic carbon-coatedgraphite, vitreous carbon-coated graphite, BN, and PBN having the sameeffect as the foregoing materials, the thermocouple and the firstprotection tube can be certainly protected from the externalenvironment.

In the thermometer comprising the first protection tube, the secondprotection tube, and the third protection tube, the first protectiontube may contain any one of Al₂O₃, MgO, CaO, BeO, ZrO₂, and HfO₂, thesecond protection tube may contain any one of graphite, C/C composite,glassy carbon, SiC, and BN, and the third protection tube may containany one of Mo, W, Ta, Nb, and Jr.

In this configuration, since the first protection tube contains any oneof Al₂O₃, MgO, CaO, BeO, ZrO₂, and HfO₂ which are stable oxides havinglow reactivity with the thermocouple and the third protection tube, thelifetime of the thermocouple can be improved. Since the secondprotection tube contains any one of graphite, C/C composite, glassycarbon, SiC, and BN having low reactivity with carbon in an atmosphereand the third protection tube, the thermocouple, the first protectiontube, and the third protection tube can be certainly protected from theexternal environment, Furthermore, since the third protection tubecontains any one of Mo, W, Ta, Nb, and Ir having low reactivity with thefirst protection tube and the second protection tube, the thermocoupleand the first protection tube can be certainly protected from theexternal environment.

In the thermometer comprising the first protection tube, the secondprotection tube, and the third protection tube, the first protectiontube may contain any one of Al₂O₃, MgO, CaO, BeO, ZrO₂, and HfO₂, thesecond protection tube may contain any one of graphite, C/C composite,glassy carbon, SiC, BN, Al₂O₃, vitreous carbon, pyrolytic carbon-coatedgraphite, vitreous carbon-coated graphite, and PBN, and the thirdprotection tube may contain any one of Mo, W, Ta, Nb, Ir, graphite, C/Ccomposite, SiC, glassy carbon, vitreous carbon, pyrolytic carbon-coatedgraphite, vitreous carbon-coated graphite, BN, and PBN

In this configuration, since the first protection tube contains any oneof Al₂O₃, MgO, CaO, BeO, ZrO₂, and HfO₂ which are stable oxides havinglow reactivity with the thermocouple and the third protection tube, thelifetime of the thermocouple can be improved. Since the secondprotection tube contains any one of the foregoing graphite, C/Ccomposite, glassy carbon, SiC, and BN, or, contains any one of Al₂O₃,vitreous carbon, pyrolytic carbon-coated graphite, vitreouscarbon-coated graphite, and PBN having the same effect as the foregoingmaterials, the thermocouple, the first protection tube, and the thirdprotection tube can be certainly protected from the externalenvironment. Furthermore, since the third protection tube contains anyone of Mo, W, Ta, Nb, and Ir, or, contains any one of graphite, C/Ccomposite, SiC, glassy carbon, vitreous carbon, pyrolytic carbon-coatedgraphite, vitreous carbon-coated graphite, BN, and PBN having the sameeffect as the foregoing materials, the thermocouple and the firstprotection tube can be certainly protected from the externalenvironment.

ADVANTAGEOUS EFFECTS OF INVENTION

The thermometer according to the one embodiment of the present inventionhas enabled the thermocouple to be protected from the externalenvironment, while preventing the protection tubes from reacting witheach other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view showing carbon atmospherethermometer according to the first embodiment.

FIG. 2 is a partial cross-sectional view showing a modification exampleof an insulating tube shown in FIG. 1, in the vicinity of thetemperature measuring junction of the thermocouple.

FIG. 3 is a partial cross-sectional view showing a modification exampleof the insulating tube shown in FIG. 1, in the vicinity of thetemperature measuring junction of the thermocouple.

FIG. 4 is a partial cross-sectional view showing a carbon atmospherethermometer according to the second embodiment.

FIG. 5 is a partial cross-sectional view showing a modification exampleof the insulating tube shown in FIG. 4, in the vicinity of thetemperature measuring junction of the thermocouple.

FIG. 6 is a partial cross-sectional view showing a modification exampleof the insulating tube shown in FIG. 4, in the vicinity of thetemperature measuring junction of the thermocouple.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Embodiments of the present invention will be described below in detailwith reference to the accompanying drawings. The thermometer of thefirst embodiment of the present invention is a thermometer using athermocouple capable of measuring temperatures under a carbon-existingatmosphere, particularly, at high temperatures over 1700° C. Multipleprotection tubes are used to protect the thermocouple from the externalcarbon atmosphere and to prevent adverse effects on an interior of afurnace and products.

As shown in FIG. 1, the carbon atmosphere thermometer 10 a of thepresent embodiment has an insulating tube 12, a thermocouple temperaturemeasuring junction 14, thermocouple wires 16, 18, a first protectiontube 20, and a second protection tube 22. The thermocouple isconstituted of the pair of thermocouple wires 16, 18, the thermocoupletemperature measuring junction 14 between the thermocouple wires 16, 18,and the insulating tube 12 covering the thermocouple wires 16, 18.

The thermocouple wires 16, 18 can be comprised, for example, of tungsten(W) and W=26% rhenium (Re), W=5% Re and W-26% Re, or, W-3% Re and W=25%Re, respectively. Or, the thermocouple wires 16, 18 can be comprised,for example, of the thermocouple wire 16 of iridium (Ir) and thethermocouple wire 18 of iridium and rhodium (IrRh), respectively. Theinsulating tube 12 is provided with axially-extending insertion holes 13in which the thermocouple wires 16, 18 are individually inserted. Theinsulating tube 12 is made of a material with excellent insulation andheat resistance and, for example, can be comprised of a ceramic such asalumina (Al₂O₃), magnesia (MgO), beryllia (BeO), or hafnia (HfO₂). Thethermocouple temperature measuring junction 14 is exposed from the tipof the insulating tube 12. FIG. 1 shows the configuration wherein thethermocouple temperature measuring junction 14 is not protected by theinsulating tube 12, but, as shown in FIG. 2, a hollow insulating tubeopen tip end 15 a with an open end face may be installed so as tosurround the surroundings of the thermocouple temperature measuringjunction 14. Or, as shown in FIG. 3, a hollow insulating tube closed tipend 15 b with a closed end face may be installed so as to surround thesurroundings of the thermocouple temperature measuring junctionFurthermore, the insertion holes 13 of the insulating tube 12 may besealed with a sealant 40 at their ends opposite to the thermocoupletemperature measuring junction 14.

The first protection tube 20 surrounds the thermocouple wires 16, 18,the thermocouple temperature measuring junction 14, and the insulatingtube 12 of the thermocouple, while at least partially spaced apart fromthe thermocouple wires 16, 18, the thermocouple temperature measuringjunction 14, and the insulating tube 12 of the thermocouple with a gap.The first protection tube 20 is comprised of any one of Mo, W, Ta, andIr having low reactivity with the thermocouple wires 16, 18 and othersof the thermocouple located inside and with the second protection tube22 located outside. One end of the first protection tube 20 is closed.The insulating tube is inserted in the first protection tube 20 so as tokeep the thermocouple temperature measuring junction 14 of thethermocouple out of contact with the inner surface of the closed end ofthe first protection tube 20. The insulating tube 12 of the thermocoupleis exposed from the end of the first protection tube 20 opposite to thethermocouple temperature measuring junction 14. The interior of thefirst protection tube 20 is filled with an inert gas such as Ar. At theend of the first protection tube 20 where the insulating tube 12 isexposed, the gap between the first protection tube 20 and the insulatingtube 12 is sealed with a sealant 31.

The second protection tube 22 surrounds the first protection tube 20,while at least partially spaced apart from the first protection tube 20with a gap. The second protection tube 22 is comprised of any one ofgraphite, C/C composite, glassy carbon, SiC, and BN having lowreactivity with the first protection tube 20 located inside and with theoutside carbon atmosphere and having airtightness. Furthermore, thesecond protection tube 22 is comprised of any one of Al₂O₃, vitreouscarbon, pyrolytic carbon-coated graphite, vitreous carbon-coatedgraphite, BN, and PBN having the same effect as the foregoing graphite,C/C composite, glassy carbon, SiC, and BN. Namely, the second protectiontube 22 may contain any one of graphite, C/C composite, glassy carbon,SiC, BN, Al₂O₃, vitreous carbon, pyrolytic carbon-coated graphite,vitreous carbon-coated graphite, and PBN. The second protection tube 22is closed at one end on the side where the thermocouple temperaturemeasuring junction 14 lies, but the second protection tube 22 may havean unclosed and open part on the opposite side to the thermocoupletemperature measuring junction 14 or the like as long as there is noinfluence on measurement of temperature and on the first protection tube20. The first protection tube 20 is inserted in the interior of thesecond protection tube 22 so as to keep the outer surface of the firstprotection tube 20 out of contact with the inner surface of the secondprotection tube 22. The space between the first protection tube 20 andthe second protection tube 22 is filled with an inert gas such as Ar. Atthe ends of the first protection tube 20 and second protection tube 22opposite to the thermocouple temperature measuring junction 14, the gapbetween the first protection tube 20 and the second protection tube 22is sealed with a sealant 33.

According to the present embodiment, the carbon atmosphere thermometer10 a has the thermocouple having the pair of thermocouple wires 16, 18,the thermocouple temperature measuring junction 14 between thethermocouple wires 16, 18, and the insulating tube 12 covering thethermocouple wires 16, 18, the first protection tube 20 surrounding thethermocouple wires 16, 18, the thermocouple temperature measuringjunction 14, and the insulating tube 12 of the thermocouple, while atleast partially spaced apart from the thermocouple wires 16, 18, thethermocouple temperature measuring junction 14, and the insulating tube12 of the thermocouple; and the second protection tube 22 surroundingthe first protection tube 20, while at least partially spaced apart fromthe first protection tube 20. The first protection tube 20 surrounds thethermocouple wires 16, 18, the thermocouple temperature measuringjunction 14, and the insulating tube 12 of the thermocouple, while atleast partially spaced apart from the thermocouple wires 16, 18, thethermocouple temperature measuring junction 14, and the insulating tube12 of the thermocouple. For this reason, it becomes feasible to protectthe thermocouple from the external environment, while preventing thethermocouple from reacting with the first protection tube 20.Furthermore, the second protection tube 22 surrounds the firstprotection tube 20, while at least partially spaced apart from the firstprotection tube 20. For this reason, it becomes feasible to protect thethermocouple and the first protection tube 20 from the externalenvironment, while preventing the first protection tube 20 from reactingwith the second protection tube 22.

The interior of the first protection tube 20 and the space between thefirst protection tube 20 and the second protection tube 22 are filledwith the inert gas. When the interior of the first protection tube 20 isfilled with the inert gas, the interior of the insulating tube 12, i.e.,an atmosphere around the thermocouple wires 16, 18 is also the inertgas. Even in the case where the insulating tube open tip end 15 a as thehollow member with the open end face or the insulating tube closed tipend 15 b as the hollow member with the closed end face is disposedaround the thermocouple temperature measuring junction 14, an atmospherearound the thermocouple temperature measuring junction 14 and thethermocouple wires 16, 18 is the inert gas. For this reason, it isfeasible to effectively prevent reaction between the thermocouple andfirst protection tube 20 and reaction between the first protection tube20 and the second protection tube 22.

Since the first protection tube 20 contains any one of Mo, W, Ta, and Irhaving low reactivity with the thermocouple and the second protectiontube 22, the lifetime of the thermocouple can be improved while thethermocouple is certainly protected from the external environment. Sincethe second protection tube 22 contains any one of graphite, C/Ccomposite, glassy carbon, SiC, and BN having low reactivity with carbonin an atmosphere and the first protection tube 20, or, contains any oneof Al₂O₃, vitreous carbon, pyrolytic carbon-coated graphite, vitreouscarbon-coated graphite, and PBN having the same effect as the foregoinggraphite, C/C composite, glassy carbon, SiC, and BN, the thermocoupleand the first protection tube 20 can be certainly protected from theexternal environment.

It is conventionally common practice to use the protection tube of astable oxide such as Al₂O₃ or MgO, particularly, in the high temperaturerange, for the purpose of protecting the wires of the thermocouple fromthe external environment. However, the oxide is reduced in thehigh-temperature carbon atmosphere to deteriorate the protection tubeand therefore it is impossible to protect the wires of the thermocoupleover a long period of time. Furthermore, the deterioration of the oxideprotection tube and exposure of a metal component due to the reductionof the oxide may adversely affect products in a thermal treatmentfurnace or in a thermal treatment step. In this manner, the conventionaltechnique does not allow stable and accurate temperature measurement tobe performed over a long period of time in the carbon-existingatmosphere at ultra-high temperatures, However, the carbon atmospherethermometer 10 a of the present embodiment can provide the thermometerthat can stably and accurately measure temperatures over a long periodof time in the high-temperature carbon atmosphere where it is difficultfor the conventional thermometers to perform measurement, and thatprevents the components of the protection tubes from affecting an objectto be thermally treated.

The second embodiment of the present invention will be described below.As shown in FIG. 4, the carbon atmosphere thermometer 10 b of thepresent embodiment is identical in the configuration of the thermocoupleincluding the thermocouple wires 16, 18 and others, the configurationexcept for the composition of the first protection tube 20, and theconfiguration of the second protection tube 22 with the firstembodiment, but is different from the first embodiment in that thethermometer 10 b further has a third protection tube 24 located outsidethe first protection tube 20 and inside the second protection tube 22and surrounding the first protection tube 20, while at least partiallyspaced apart from the first protection tube 20 and the second protectiontube 22. In the present embodiment, the first protection tube 20 iscomprised of any one of Mo, W, Ta, and Ir having low reactivity with thethermocouple wires 16, 18 and others of the thermocouple located insideand with the third protection tube located outside. The third protectiontube 24 is comprised of any one of Mo, W, Ta, Nb, and Ir having lowreactivity with the inside first protection tube 20 and the outsidesecond protection tube 22. Furthermore, the third protection tube 24 iscomprised of any one of graphite, C/C composite, SiC, glassy carbon,vitreous carbon, pyrolytic carbon-coated graphite, vitreouscarbon-coated graphite, BN, and PBN having the same effect as theforegoing Mo, W, Ta, Nb, and Ir. Namely, the third protection tube 24may contain any one of Mo, W, Ta, Nb, Ir, graphite, C/C composite, SIC,glassy carbon, vitreous carbon, pyrolytic carbon-coated graphite,vitreous carbon-coated graphite, BN, and PBN.

Or, in the present embodiment, the first protection tube 20 may becomprised of any one of Al₂O₃, MgO, CaO, BeO, ZrO₂, and HfO₂ which arestable oxides having low reactivity with the inside thermocouple wires16, 18 and others of the thermocouple and with the outside thirdprotection tube 24. In this case, the third protection tube 24 iscomprised of any one of Mo, W, Ta, Nb, and Ir having low reactivity withthe inside first protection tube 20 and the outside second protectiontube 22. Furthermore, the third protection tube 24 is comprised of anyone of graphite, C/C composite, SiC, glassy carbon, vitreous carbon,pyrolytic carbon-coated graphite, vitreous carbon-coated graphite, BN,and PBN having the same effect as the foregoing Mo, W, Ta, Nb, and Jr.Namely, the third protection tube 24 may contain any one of Mo, W, Ta,Nb, Ir, graphite, C/C composite, SiC, glassy carbon, vitreous carbon,pyrolytic carbon-coated graphite, vitreous carbon-coated graphite, BN,and PBN. The third protection tube 24 is closed at one end on the sidewhere the thermocouple temperature measuring junction 14 lies, but ifthe second protection tube 22 is closed, the one end off the thirdprotection tube 24 may be unclosed and open. Furthermore, at least oneend of the third protection tube 24 and the second protection tube 22opposite to the thermocouple temperature measuring junction 14 may havean unclosed and open part. Namely, at least one end of the thirdprotection tube 24 and the second protection tube 22 opposite to thethermocouple temperature measuring junction 14 may be open as long asthere is no influence on the measurement of temperature and the firstprotection tube 20.

The space between the first protection tube 20 and the third protectiontube 24 and the space between the second protection tube 22 and thethird protection tube 24 are filled with an inert gas such as Ar. At theends of the first protection tube 20 and the third protection tube 24opposite to the thermocouple temperature measuring junction 14, the gapbetween the first protection tube 20 and the third protection tube 24 issealed with the sealant 33. At the ends of the second protection tube 22and the third protection tube 24 opposite to the thermocoupletemperature measuring junction 14, the gap between the second protectiontube 22 and the third protection tube 24 is sealed with a sealant 35. Asin the first embodiment, the interior of the first protection tube 20 isfilled with the inert gas such as Ar. At the end of the first protectiontube 20 where the insulating tube 12 projects out, the gap between thefirst protection tube 20 and the insulating tube 12 is filled with thesealant 31. FIG. 4 shows the configuration wherein the thermocoupletemperature measuring junction 14 is not protected by the insulatingtube 12, but, as shown in FIG. 5, the hollow insulating tube open tipend 15 a with the open end face may be installed so as to surround thesurroundings of the thermocouple temperature measuring junction 14. Or,as shown in FIG. 6, the hollow insulating tube closed tip end 15 b withthe closed end face may be installed so as to surround the surroundingsof the thermocouple temperature measuring junction 14. Furthermore, theinsertion holes 13 of the insulating tube 12 at their ends opposite tothe thermocouple temperature measuring junction 14 are sealed with thesealant 40.

In the present embodiment, the thermometer further has the thirdprotection tube 24 located outside the first protection tube 20 andinside the second protection tube 22 and surrounding the firstprotection tube 20, while at least partially spaced apart from the firstprotection tube 20 and the second protection tube 22. For this reason,while the first protection tube 20 and second protection tube 22 areprevented from reacting with the third protection tube 24, the firstprotection tube 20 can be effectively prevented from reacting with thesecond protection tube 22.

In the present embodiment, the interior of the first protection tube 20,the space between the first protection tube 20 and the third protectiontube 24, and the space between the second protection tube 22 and thethird protection tube 24 are filled with the inert gas. As describedabove, when the interior of the first protection tube 20 is filled withthe inert gas, the interior of the insulating tube 12, i.e., theatmosphere around the thermocouple wires 16, 18 is also the inert gas.

Even in the case where the insulating tube open tip end 15 a as thehollow member with the open end face or the insulating tube closed tipend 15 b as the hollow member with the closed end face is disposedaround the thermocouple temperature measuring junction 14, theatmosphere around the thermocouple temperature measuring junction 14 andthe thermocouple wires 16, 18 is also the inert gas. For this reason, itis feasible to effectively prevent reaction between the thermocouple andfirst protection tube 20, reaction between the first protection tube 20and third protection tube 24, and reaction between the second protectiontube 22 and third protection tube 24.

In the present embodiment, since the first protection tube 20 containsany one of Mo, W, Ta, and Ir having the low reactivity with thethermocouple and third protection tube 24, the lifetime of thethermocouple can be improved. Furthermore, since the second protectiontube 22 contains any one of graphite, CIC composite, glassy carbon, SiC,and BN with the low reactivity with carbon in the atmosphere and thethird protection tube 24, or, contains any one of Al₂O₃, vitreouscarbon, pyrolytic carbon-coated graphite, vitreous carbon-coatedgraphite, and PBN, it can certainly protect the thermocouple, firstprotection tube 20, and third protection tube 24 from the externalenvironment. Further more, since the third protection tube 24 containsany one of Mo, W, Ta, Nb, and Ir with the low reactivity with the firstprotection tube 20 and the second protection tube 22, or, contains anyone of graphite, C/C composite, SiC, glassy carbon, vitreous carbon,pyrolytic carbon-coated graphite, vitreous carbon-coated graphite, BN,and PBN, it can certainly protect the thermocouple and first protectiontube 20 from the external environment.

Or, since the first protection tube 20 contains any one of Al₂O₃, MgO,CaO, BeO, ZrO₂, and HfO₂ which are stable oxides having the lowreactivity with the thermocouple and the third protection tube 24, thelifetime of the thermocouple can be improved. Since the secondprotection tube 22 contains any one of graphite, C/C composite, glassycarbon, SiC, and BN having the low reactivity with carbon in theatmosphere and the third protection tube 24, or, contains any one ofAl₂O₃, vitreous carbon, pyrolytic carbon-coated graphite, vitreouscarbon-coated graphite, BN, and PBN, it can certainly protect thethermocouple, first protection tube 20, and third protection tube 24from the external environment. Furthermore, the third protection tube 24contains any one of Mo, W, Ta, Nb, and Ir having the low reactivity withthe first protection tube 20 and the second protection tube 22, or,contains any one of graphite, C/C composite, SIC, glassy carbon,vitreous carbon, pyrolytic carbon-coated graphite, vitreouscarbon-coated graphite, BN, and PBN, it can certainly protect thethermocouple and first protection tube 20 from the external environment.

The present invention does not have to be limited only to the aboveembodiments, but can have a variety of modifications. For example, theabove embodiments were described with focus on the two configurations,the configuration with the double protection tubes of the firstprotection tube 20 surrounding the thermocouple and the secondprotection tube 22 surrounding the first protection tube; and theconfiguration with the triple protection tubes of the first protectiontube surrounding the thermocouple, the third protection tube 24surrounding the first protection tube, and the second protection tube 22surrounding the third protection tube 24, but the present invention doesnot have to be limited only to these but also includes configurationswith four or more protection tubes within the scope of the invention. Itis also possible to freely change the thicknesses, lengths, andcompositions of the respective protection tubes. The reason why thethicknesses and lengths are changeable is that when the thicknesses ofthe protection tubes are smaller, heat becomes easier to transfer,improving the temperature response. On the other hand, when thethicknesses are larger and, particularly, when the materials of theadjacent protection tubes are different, progress of reaction can bedelayed more. Concerning the lengths of the protection tubes, when theprotection tubes of necessary lengths are disposed at necessarylocations only, manufacture becomes easier and cost can be lowered. Forexample, in a case where the thermocouple is likely to sufferabnormality such as deterioration or contamination, at a specific partof a temperature measurement target furnace, the protection tubes can belocated only in the range of influence thereof, whereby the influencecan be suppressed and whereby manufacture becomes easier, so as toreduce cost.

EXAMPLES

Next, the embodiments of the present invention will be described in moredetail by comparison between Examples indicative of the experimentresults of temperature measurement by means of the thermocouples of thepresent invention and Comparative Examples indicative of the experimentresults of temperature measurement by means of the conventionalthermocouples to measure a carbon-existing atmosphere at hightemperatures. C- or Si-existing atmospheres around 2000° C. areextremely harsh ambiences where most of metals become carbonized orlower their melting point to deteriorate. In the case of thethermocouple using platinum, when it is used in a harsh environmentaround its upper limit temperature, even in an air atmosphere, itslifetime can reduce to about 50 hours; therefore, a criterion forjudgment of operable time was determined to be 50 hours.

For measuring temperatures in such atmospheres, it is a matter of coursethat an appropriate thermocouple must be selected, and selection of theprotection tubes as constituents is also important. We clearly showedthe protection tubes and structures thereof enabling the temperaturemeasurement even in such harsh atmospheres.

Example 1

In the present example, the thermometer used was one according to thefirst embodiment. A set of graphite (second protection tube)/Ir (firstprotection tube)/HfO₂ (insulating tube)/Ir and Ir-40 wt % Rh (wires)thermocouple constituting the thermometer was immersed by 20 mm in anSi-based melt in a furnace comprised of a furnace material of graphite,and temperature measurement of this melt was carried out at 1900° C. inan Ar atmosphere. The graphite (second protection tube) had the outsidediameter of 10 mm and the thickness of 1.75 mm, the Ir (first protectiontube) had the outside diameter of 4.8 mm and the thickness of 0.5 mm,the HfO₂ (insulating tube) was a two-hole tube having the outsidediameter of 3.2 mm and the inside diameter of 0.9 mm, and the Ir andIr-40 wt % Rh (wires) each had the diameter of 0.5 mm. The graphite(second protection tube) was arranged without isolation of inside andoutside and thus the interior atmosphere thereof was identical with thein-furnace atmosphere. In addition, the interior of the Ir (firstprotection tube) was filled with Ar so as to be isolated from theoutside. Under the above conditions, the temperature measurement wasstarted and after a lapse of 63.7 hours, the measurement wasdiscontinued because the thermocouple exhibited an abnormality ofthermoelectromotive force. It was confirmed that this thermocouple couldbe used even over 50 hours which was the criterion fortemperature-measurable time. This thermocouple was detached to checkconditions of the members and roughness of surface was recognized in therange of about 20 mm from the tip of the Ir (first protection tube).

Example 2

In the present example, the thermometer used was one according to thefirst embodiment. A set of vitreous carbon (second protection tube)/Ir(first protection tube)/HfO₂ (insulating tube)/Ir and Ir-40 wt % Rh(wires) thermocouple constituting the thermometer was immersed by 20 mmin an Si-based melt in a furnace comprised of a furnace material ofgraphite, and temperature measurement of this melt was carried out at1900° C. in an Ar atmosphere. The vitreous carbon (second protectiontube) had the outside diameter of 10 mm and the thickness of 1.75 mm,the Ir (first protection tube) had the outside diameter of 4.8 mm andthe thickness of 0.5 mm, the HfO₂ (insulating tube) was a two-hole tubehaving the outside diameter of 3.2 mm and the inside diameter of 0.9 mm,and the Ir and Ir-40 wt % Rh (wires) each had the diameter of 0.5 mm.The vitreous carbon (second protection tube) was arranged withoutisolation of inside and outside and thus the interior atmosphere thereofwas identical with the in-furnace atmosphere. In addition, the interiorof the Ir (first protection tube) was filled with Ar so as to beisolated from the outside. Under the above conditions, the temperaturemeasurement was started and the temperature measurement was terminatedafter a lapse of 100 hours. During the measurement, there was noabnormality of thermoelectromotive force recognized. In observation ofappearance after the measurement, slight discoloration (light brown) wasobserved in the range of 20 mm from the tip of the Ir (first protectiontube), but there was no other abnormality recognized.

Example 3

In the present example, the thermometer used was one according to thefirst embodiment. A set of pyrolytic carbon-coated graphite (secondprotection tube)/Ir (first protection tube)/HfO₂ (insulating tube)/Irand Ir-40 wt % Rh (wires) thermocouple constituting the thermometer wasimmersed by 20 mm in an Si-based melt in a furnace comprised of afurnace material of graphite, and temperature measurement of this meltwas carried out at 1900° C. in an Ar atmosphere. The pyrolyticcarbon-coated graphite (second protection tube) had the outside diameterof 10 mm and the thickness of 1.75 mm, the Ir (first protection tube)had the outside diameter of 4.8 mm and the thickness of 0.5 mm, the HfO₂(insulating tube) was a two-hole tube having the outside diameter of 3.2mm and the inside diameter of 0.9 mm, and the Ir and Ir-4 0wt % Rh(wires) each had the diameter of 0.5 mm. The pyrolytic carbon-coatedgraphite (second protection tube) was arranged without isolation ofinside and outside and thus the interior atmosphere thereof wasidentical with the in-furnace atmosphere. In addition, the interior ofthe Ir (first protection tube) was filled with Ar so as to be isolatedfrom the outside. Under the above conditions, the temperaturemeasurement was started and the temperature measurement was terminatedafter a lapse of 100 hours. During the measurement, there was noabnormality of thermoelectromotive force recognized. In observation ofappearance after the measurement, slight discoloration (light brown) androughness of surface were observed in the range of 20 mm from the tip ofthe Ir (first protection tube), but there was no other abnormalityrecognized.

Example 4

In the present example, the thermometer used was one according to thefirst embodiment. A set of vitreous carbon-coated graphite (secondprotection tube)/Ir (first protection tube)/HfO₂ (insulating tube)/Irand Ir-40 wt % Rh (wires) thermocouple constituting the thermometer wasimmersed by 20 mm in an Si-based melt in a furnace comprised of afurnace material of graphite, and temperature measurement of this meltwas carried out at 1900° C. is an Ar atmosphere. The vitreouscarbon-coated graphite (second protection tube) had the outside diameterof 10 mm and the thickness of 135 min, the Ir (first protection tube)had the outside diameter of 4.8 mm and the thickness of 0.5 mm, the HfO2(insulating tube) was a two-hole tube having the outside diameter of 3.2mm and the inside diameter of 0.9 mm, and the Ir and Ir-40 wt % Rh(wires) each had the diameter of 0.5 mm. The vitreous carbon-coatedgraphite (second protection tube) was arranged without isolation ofinside and outside and thus the interior atmosphere thereof wasidentical with the in-furnace atmosphere. In addition, the interior ofthe Ir (first protection tube) was filled with Ar so as to be isolatedfrom the outside. Under the above conditions, the temperaturemeasurement was started and the temperature measurement was terminatedafter a lapse of 100 hours. During the measurement, there was noabnormality of thermoelectromotive force recognized. In observation ofappearance after the measurement, slight discoloration (light brown) androughness of surface were observed in the range of 20 mm from the tip ofthe Ir (first protection tube), but there was no other abnormalityrecognized.

Example 5

In the present example, the thermometer used was one according to thefirst embodiment. A set of BN (second protection tube)/Ir (firstprotection tube)/HfO₂ (insulating tube)/Ir and Ir-40 wt % Rh (wires)thermocouple constituting the thermometer was immersed by 20 mm in anSi-based melt in a furnace comprised of a furnace material of graphite,and temperature measurement of this melt was carried out at 1900° C. inan Ar atmosphere. The BN (second protection tube) had the outsidediameter of 10 mm and the thickness of 1 mm, the Ir (first protectiontube) had the outside diameter of 4.8 mm and the thickness of 0.5 mm,the HfO₂ (insulating tube) was a two-hole tube having the outsidediameter of 32 mm and the inside diameter of 0.9 mm, and the Ir andIr-40 wt % Rh (wires) each had the diameter of 0.5 mm. The BN (secondprotection tube) was arranged without isolation of inside and outsideand thus the interior atmosphere thereof was identical with thein-furnace atmosphere. In addition, the interior of the Ir (firstprotection tube) was filled with Ar so as to be isolated from theoutside,

Under the above conditions, the temperature measurement was started andthe temperature measurement was terminated after a lapse of 100 hours,During the measurement, there was no abnormality of thermoelectromotiveforce recognized. In observation of appearance after the measurement,there was no particular abnormality recognized, either.

Example 6

In the present example, the thermometer used was one according to thefirst embodiment. A set of Al2O3 (second protection tube)/Ir (firstprotection tube)/HfO2 (insulating tube)/Ir and Ir-40 wt % Rh (wires)thermocouple constituting the thermometer was immersed by 20 mm in anSi-based melt in a furnace comprised of a furnace material of graphite,and temperature measurement of this melt was carried out at 1800° C. inan Ar atmosphere. The Al2O3 (second protection tube) had the outsidediameter of 10 mm and the thickness of 2 mm, the Ir (first protectiontube) had the outside diameter of 4.8 mm and the thickness of 0.5 mm,the HfO2 (insulating tube) was a two-hole tube having the outsidediameter of 3.2 mm and the inside diameter of 0.9 mm, and the Ir andIr=40 wt % Rh (wires) each had the diameter of 0.5 mm. The Al2O3 (secondprotection tube) was arranged without isolation of inside and outsideand thus the interior atmosphere thereof was identical with thein-furnace atmosphere. In addition, the interior of the Ir (firstprotection tube) was filled with Ar so as to be isolated from theoutside. Under the above conditions, the temperature measurement wasstarted and the temperature measurement was terminated after a lapse of100 hours. During the measurement, there was no abnormality ofthermoelectromotive force recognized. In observation of appearance afterthe measurement, slight discoloration (light brown) and roughness ofsurface were observed in the range of 20 mm from the tip of the Ir(first protection tube), but there was no other abnormality recognized.

Example 7

In the present example, the thermometer used was one according to thesecond embodiment. A set of graphite (second protection tube)/vitreouscarbon (third protection tube)/Ir (first protection tube)/HfO₂(insulating tube)/Ir and Ir-40 wt % Rh (wires) thermocouple constitutingthe thermometer was immersed by 20 mm in an Si-based melt in a furnacecomprised of a furnace material of graphite, and temperature measurementof this melt was carried out at 1900° C. in an Ar atmosphere. Thegraphite (second protection tube) had the outside diameter of 30 mm andthe thickness of 10 mm, the vitreous carbon (third protection tube) hadthe outside diameter of 8 mm and the thickness of 1 mm, the Ir (firstprotection tube) had the outside diameter of 4.8 mm and the thickness of(15 mm, the HfO₂ (insulating tube) was a two-hole tube having theoutside diameter of 3.2 mm and the inside diameter of 0.9 mm, and the Irand Ir-40 wt % Rh (wires) each had the diameter of 0.5 mm. The graphite(second protection tube) and vitreous carbon (third protection tube)were arranged without isolation of inside and outside and thus theinterior atmosphere thereof was identical with the in-furnaceatmosphere. In addition, the interior of the Ir (first protection tube)was filled with Ar so as to be isolated from the outside. Under theabove conditions, the temperature measurement was started and thetemperature measurement was terminated after a lapse of 100 hours.During the measurement, there was no abnormality of thermoelectromotiveforce recognized. In observation of appearance after the measurement,there was no particular abnormality recognized, either.

Example 8

In the present example, the thermometer used was one according to thesecond embodiment. A set of graphite (second protection tube)/pyrolyticcarbon-coated graphite (third protection tube)/Ir (first protectiontube)/HfO₂ (insulating tube)/Ir and Ir-40 wt % Rh (wires) thermocoupleconstituting the thermometer was immersed by 20 mm in an Si-based meltin a furnace comprised of a furnace material of graphite, andtemperature measurement of this melt was carried out at 1900° C. in anAr atmosphere. The graphite (second protection tube) had the outsidediameter of 30 mm and the thickness of 10 mm, the pyrolyticcarbon-coated graphite (third protection tube) had the outside diameterof 8 mm and the thickness of 1 mm, the Ir (first protection tube) hadthe outside diameter of 4.8 mm and the thickness of 0.5 mm, the HfO₂(insulating tube) was a two-hole tube having the outside diameter of 12mm and the inside diameter of 0.09 mm, and the Ir and Ir-40 wt % Rh(wires) each had the diameter of 0.5 mm. The graphite (second protectiontube) and pyrolytic carbon-coated graphite (third protection tube) werearranged without isolation of inside and outside and thus the interioratmosphere thereof was identical with the in-furnace atmosphere. Inaddition, the interior of the Ir (first protection tube) was filled withAr so as to be isolated from the outside, Under the above conditions,the temperature measurement was started and the temperature measurementwas terminated after a lapse of 100 hours. During the measurement, therewas no abnormality of thermoelectromotive force recognized. Inobservation of appearance after the measurement, slight discoloration(light brown) was observed in the range of 20 nun from the tip of the Ir(first protection tube), but there was no other abnormality recognized.

Example 9

In the present example, the thermometer used was one according to thesecond embodiment. A set of graphite (second protection tube)/vitreouscarbon-coated graphite (third protection tube)/Ir (first protectiontube)/HfO2 (insulating tube)/Ir and Ir=40 wt % Rh (wires) thermocoupleconstituting the thermometer was immersed by 20 mm in an Si-based meltin a furnace comprised of a furnace material of graphite, andtemperature measurement of this melt was carried out at 1900° C. in anAr atmosphere. The graphite (second protection tube) had the outsidediameter of 30 mm and the thickness of 10 mm, the vitreous carbon-coatedgraphite (third protection tube) had the outside diameter of 8 mm andthe thickness of 1 mm, the Ir (first protection tube) had the outsidediameter of 4.8 mm and the thickness of 0.5 mm, the HfO2 (insulatingtube) was a two-hole tube having the outside diameter of 3.2 mm and theinside diameter of 0.9 mm, and the Ir and Ir-40 wt % Rh (wires) each hadthe diameter of 0.5 mm. The graphite (second protection tube) andvitreous carbon-coated graphite (third protection tube) were arrangedwithout isolation of inside and outside and thus the interior atmospherethereof was identical with the in furnace atmosphere. In addition, theinterior of the Ir (first protection tube) was filled with Ar so as tobe isolated from the outside. Under the above conditions, thetemperature measurement was started and the temperature measurement wasterminated after a lapse of 100 hours. During the measurement, there wasno abnormality of thermoelectromotive force recognized. In observationof appearance after the measurement, slight discoloration (light brown)was observed in the range of 20 mm from the tip of the Ir (firstprotection tube), but there was no other abnormality recognized.

Example 10

In the present example, the thermometer used was one according to thesecond embodiment. A set of graphite (second protection tube)/BN (thirdprotection tube)/Ir (first protection tube)/HfO₂ (insulating tube)/Irand Ir-40 wt % Rh (wires) thermocouple constituting the thermometer wasimmersed by 20 mm in an Si-based melt in a furnace comprised of afurnace material of graphite, and temperature measurement of this meltwas carried out at 1900° C. in an Ar atmosphere. The graphite (secondprotection tube) had the outside diameter of 30 mm and the thickness of10 mm, the BN (third protection tube) had the outside diameter of 8 mmand the thickness of 0.8 mm, the Ir (first protection tube) had theoutside diameter of 4.8 mm and the thickness of 0.5 mm, the HfO₂(insulating tube) was a two-hole tube having the outside diameter of 3.2mm and the inside diameter of 0.9 mm, and the Ir and Ir-40 wt % Rh(wires) each had the diameter of 0.5 mm. The graphite (second protectiontube) and pyrolytic carbon-coated graphite (third protection tube) werearranged without isolation of inside and outside and thus the interioratmosphere thereof was identical with the in-furnace atmosphere. Inaddition, the interior of the Ir (first protection tube) was filled withAr so as to be isolated from the outside. Under the above conditions,the temperature measurement was started and the temperature measurementwas terminated after a lapse of 100 hours. During the measurement, therewas no abnormality of thermoelectromotive force recognized. Inobservation of appearance after the measurement, there was no particularabnormality recognized, either.

Example 11

In the present example, the thermometer used was one according to thefirst embodiment. A set of vitreous carbon (second protection tube)/Mo(first protection tube)/HfO₂ (insulating tube)/Ir and Ir-40 wt % Rh(wires) thermocouple constituting the thermometer was immersed by 20 mmin an Si-based melt in a furnace comprised of a furnace material ofgraphite, and temperature measurement of this melt was carried out at1900° C. in an Ar atmosphere. The vitreous carbon (second protectiontube) had the outside diameter of 10 mm and the thickness of 1.75 mm,the Mo (first protection tube) had the outside diameter of 4.8 mm andthe thickness of 0.5 mm, the HfO₂ (insulating tube) was a two-hole tubehaving the outside diameter of 3.2 mm and the inside diameter of 0.9 mm,and the Ir and Ir-40 wt % Rh (wires) each had the diameter of 0.5 mm.The vitreous carbon (second protection tube) was arranged withoutisolation of inside and outside and thus the interior atmosphere thereofwas identical with the in-furnace atmosphere. In addition, the interiorof the Mo (first protection tube) was filled with Ar so as to beisolated from the outside. Under the above conditions, the temperaturemeasurement was started and the temperature measurement was terminatedafter a lapse of 100 hours. During the measurement, there was noabnormality of thermoelectromotive force recognized. In observation ofappearance after the measurement, adhesion of black foreign matteroriginating in the vitreous carbon (second protection tube) was observedin the range of 20 mm from the tip of the Mo (first protection tube),but there was no leakage of Mo (first protection tube) recognized.

Example 12

In the present example, the thermometer used was one according to thefirst embodiment. A set of BN (second protection tube)/Mo (firstprotection tube)/HfO₂ (insulating tube)/Ir and Ir-40 wt % Rh (wires)thermocouple constituting the thermometer was immersed by 20 mm in anSi-based melt in a furnace comprised of a furnace material of graphite,and temperature measurement of this melt was carried out at 1900° C. inan Ar atmosphere. The BN (second protection tube) had the outsidediameter of 10 mm and the thickness of 1 mm, the Ir (first protectiontube) had the outside diameter of 4.8 mm and the thickness of 0.5 mm,the HfO₂ (insulating tube) was a two-hole tube having the outsidediameter of 3.2 mm and the inside diameter of 0.9 mm, and the Ir andIr-40 wt % Rh (wires) each had the diameter of 0.5 mm. The BN (secondprotection tube) was arranged without isolation of inside and outsideand thus the interior atmosphere thereof was identical with thein-furnace atmosphere. In addition, the interior of the Mo (firstprotection tube) was filled with Ar so as to be isolated from theoutside. Under the above conditions, the temperature measurement wasstarted and the temperature measurement was terminated after a lapse of100 hours. During the measurement, there was no abnormality ofthermoelectromotive force recognized. In observation of appearance afterthe measurement, slight roughness of surface was observed in the rangeof 20 mm from the tip but there was no other abnormality recognized.

Example 13

In the present example, the thermometer used was one according to thefirst embodiment. A set of vitreous carbon (second protection tube)/Ta(first protection tube)/HfO₂ (insulating tube)/Ir and Ir-40 wt % Rh(wires) thermocouple constituting the thermometer was immersed by 20 mmin an Si-based melt in a furnace comprised of a furnace material ofgraphite, and temperature measurement of this melt was carried out at1900° C. in an Ar atmosphere. The vitreous carbon (second protectiontube) had the outside diameter of 10 mm and the thickness of 1.75 mm,the Ta (first protection tube) had the outside diameter of 4.8 mm andthe thickness of 0.5 mm, the HfO₂ (insulating tube) was a two-hole tubehaving the outside diameter of 3.2 mm and the inside diameter of 0.9 mm,and the Ir and Ir-40 wt % Rh (wires) each had the diameter of 0.5 mm.The vitreous carbon (second protection tube) was arranged withoutisolation of inside and outside and thus the interior atmosphere thereofwas identical with the in-furnace atmosphere. In addition, the interiorof the Ta (first protection tube) was filled with Ar so as to beisolated from the outside. Under the above conditions, the temperaturemeasurement was started and the temperature measurement was terminatedafter a lapse of 100 hours.

During the measurement, there was no abnormality of thermoelectromotiveforce recognized. In observation of appearance after the measurement,there was no particular abnormality recognized, either.

Example 14

In the present example, the thermometer used was one according to thefirst embodiment. A set of BN (second protection tube)/Ta (firstprotection tube)/HfO₂ (insulating tube)/Ir and Ir-40 wt % Rh (wires)thermocouple constituting the thermometer was immersed by 20 mm in anSi-based melt in a furnace comprised of a furnace material of graphite,and temperature measurement of this melt was carried out at 1900° C. inan Ar atmosphere. The BN (second protection tube) had the outsidediameter of 10 mm and the thickness of 1 mm, the Ir (first protectiontube) had the outside diameter of 4.8 mm and the thickness of 0.5 mm,the HfO₂ (insulating tube) was a two-hole tube having the outsidediameter of 3.2 mm and the inside diameter of 0.9 mm, and the Ir andIr-40 wt % Rh (wires) each had the diameter of 0.5 mm. The BN (secondprotection tube) was arranged without isolation of inside and outsideand thus the interior atmosphere thereof was identical with thein-furnace atmosphere. In addition, the interior of the Ta (firstprotection tube) was filled with Ar so as to be isolated from theoutside. Under the above conditions, the temperature measurement wasstarted and the temperature measurement was terminated after a lapse of100 hours. During the measurement, there was no abnormality ofthermoelectromotive force recognized. In observation of appearance afterthe measurement, there was no particular abnormality recognized, either.

COMPARATIVE EXAMPLE 1

In the present example, the thermometer used was one obtained byexcluding the second protection tube from the thermometer according tothe first embodiment. A set of Ir (first protection tube)/HfO₂(insulating tube)/Ir and Ir-40 wt % Rh (wires) thermocouple constitutingthe thermometer was immersed by 20 mm in an Si-based melt in a furnacecomprised of a furnace material of graphite, and temperature measurementof this melt was carried out at 1900° C. in an Ar atmosphere. The Ir(first protection tube) had the outside diameter of 4.8 mm and thethickness of 0.5 mm, the HfO₂ (insulating tube) was a two-hole tubehaving the outside diameter of 3.2 mm and the inside diameter of 0.9 mm,and the Ir and Ir-40 wt % Rh (wires) each had the diameter of 0.5 mm.The interior of the Ir (first protection tube) was filled with Ar. Underthe above conditions, the temperature measurement was started and aftera lapse of 7.6 hours, the measurement was discontinued because thethermocouple exhibited an abnormality of thermoelectromotive force.Thereafter, the thermocouple was detached to check conditions of themembers and roughness of surface was recognized in the range of about 20mm from the tip of the Ir (first protection tube).

COMPARATIVE EXAMPLE 2

In the present example, the thermometer used was one obtained byexcluding the second protection tube from the thermometer according tothe first embodiment. A set of Ir (first protection tube)/HfO2(insulating tube)/Ir and Ir-40 wt % Rh (wires) thermocouple constitutingthe thermometer was immersed by 20 mm in an Si-based melt in a furnacecomprised of a furnace material of graphite, and temperature measurementof this melt was carried out at 1800° C. in an Ar atmosphere. The Ir(first protection tube) had the outside diameter of 4.8 mm and thethickness of 0.5 mm, the HfO2 (insulating tube) was a two-hole tubehaving the outside diameter of 3.2 mm and the inside diameter of 0.9 mm,and the Ir and Ir=40 wt % Rh (wires) each had the diameter of 0.5 mm.The interior of the Ir (first protection tube) was filled with Ar. Underthe above conditions, the temperature measurement was started and aftera lapse of 8.1 hours, the measurement was discontinued because thethermocouple exhibited an abnormality of thermoelectromotive force.Thereafter, the thermocouple was detached to check conditions of themembers and roughness of surface was recognized in the range of about 20mm from the tip of the Ir (first protection tube).

REFERENCE SIGNS LIST

10 a, 10 b carbon atmosphere thermometers; 12 insulating tube; 13insertion holes; 14 thermocouple temperature measuring junction; 15 ainsulating tube open tip end; 15 b insulating tube closed tip end; 16,18 thermocouple wires; 20 first protection tube; 22 second protectiontube; 24 third protection tube; 31, 33, 35 sealants; 40 sealant.

1. A thermometer comprising: a thermocouple having a pair of wires, atemperature measuring junction between the wires, and an insulatorcovering the wires; a first protection tube surrounding the wires, thetemperature measuring junction, and the insulator of the thermocouple,while at least partially spaced apart from the wires, the temperaturemeasuring junction, and the insulator of the thermocouple; and a secondprotection tube surrounding the first protection tube, while at leastpartially spaced apart from the first protection tube.
 2. Thethermometer according to claim 1, wherein at least either of an interiorof the first protection tube or a space between the first protectiontube and the second protection tube is filled with an inert gas.
 3. Thethermometer according to claim 1, further comprising a third protectiontube located outside the first protection tube and inside the secondprotection tube and surrounding the first protection tube, while atleast partially spaced apart from the first protection tube and thesecond protection tube.
 4. The thermometer according to claim 3, whereinat least any one of an interior of the first protection tube, a spacebetween the first protection tube and the third protection tube, and aspace between the second protection tube and the third protection tubeis filled with an inert gas.
 5. The thermometer according to claim 1,wherein the first protection tube contains any one of Mo, W, Ta, and Irand the second protection tube contains any one of graphite, C/Ccomposite, glassy carbon, SiC, and BN.
 6. The thermometer according toclaim 1, wherein the first protection tube contains any one of Mo, W,Ta, and Ir and the second protection tube contains any one of graphite,C/C composite, glassy carbon, SiC, BN, Al2O3, vitreous carbon, pyrolyticcarbon-coated graphite, vitreous carbon-coated graphite, and PBN.
 7. Thethermometer according to claim 3, wherein the first protection tubecontains any one of Mo, W, Ta, and Ir, the second protection tubecontains any one of graphite, C/C composite, glassy carbon, SiC, and BN,and the third protection tube contains any one of Mo, W, Ta, Nb, and Ir.8. The thermometer according to claim 3, wherein the first protectiontube contains any one of Mo, W, Ta, and Ir, the second protection tubecontains any one of graphite, C/C composite, glassy carbon, SiC, BN,Al₂O₃, vitreous carbon, pyrolytic carbon-coated graphite, vitreouscarbon-coated graphite, and PBN, and the third protection tube containsany one of Mo, W, Ta, Nb, Ir, graphite, C/C composite, SiC, glassycarbon, vitreous carbon, pyrolytic carbon-coated graphite, vitreouscarbon-coated graphite, BN, and PBN.
 9. The thermometer according toclaim 3, wherein the first protection tube contains any one of Al2O3,MgO, CaO, BeO, ZrO2, and HfO2, the second protection tube contains anyone of graphite, C/C composite, glassy carbon, SiC, and BN, and thethird protection tube contains any one of Mo, W, Ta, Nb, and Ir.
 10. Thethermometer according to claim 3, wherein the first protection tubecontains any one of Al2O3, MgO, CaO, BeO, ZrO2, and HfO2, the secondprotection tube contains any one of graphite, C/C composite, glassycarbon, SiC, BN, Al2O3, vitreous carbon, pyrolytic carbon-coatedgraphite, vitreous carbon-coated graphite, and PBN, and the thirdprotection tube contains any one of Mo, W, Ta, Nb, Ir, graphite, C/Ccomposite, SiC, glassy carbon, vitreous carbon, pyrolytic carbon-coatedgraphite, vitreous carbon-coated graphite, BN, and PBN.